Comparison of external apical root resorption in maxillary anterior teeth following en-masse versus two-step retraction: a 3D volumetric CBCT-based randomized controlled trial.

OBJECTIVES: Comparison of external apical root resorption (EARR) between space-closure techniques remains inconsistent due to 2D imaging limitations. This study aimed to quantify and compare EARR in maxillary anterior teeth following en-masse versus two-step retraction using 3D cone-beam computed tomography (CBCT). METHODS: This prospective randomized controlled trial included 60 male and female patients (mean age 19.87 ± 4.01 years) requiring bilateral maxillary first premolar extractions and maximum anchorage. Participants were randomly allocated to en-masse retraction (210 g/side) or two-step retraction (70 g canine retraction, then 140 g incisor retraction). CBCT scans were obtained before (T1) and after (T2) space closure. Three-dimensional root models were reconstructed using Mimics software. Linear root length and volumetric changes were compared (Mann-Whitney U test; p < 0.05). RESULTS: Both groups exhibited statistically significant reductions (p < 0.001) in root length (two-step: -0.56 ± 0.09 mm; en-masse: -0.57 ± 0.11 mm) and root volume (two-step: -8.88 ± 3.24 mm3; en-masse: -10.12 ± 4.49 mm3). No statistically significant differences were observed between techniques for any tooth or overall mean values (p > 0.05). Lateral incisors showed the greatest linear resorption in the two-step group, while volumetric reductions were substantial across central incisors and canines. CONCLUSION: En-masse and two-step space closure produce comparable linear and volumetric resorption; neither technique confers a protective or detrimental advantage regarding EARR. CLINICAL RELEVANCE: Neither retraction technique increases the risk of EARR, allowing clinicians to select either approach without concern for differential root resorption when biomechanical control is appropriately maintained. TRIAL REGISTRATION: The trial was registered at ClinicalTrials.gov: NCT05606185 on October 31, 2022 (first posted: November 4, 2022; ( https://clinicaltrials.gov/study/NCT05606185 ).